Aqueous eutectic hydrogel electrolytes enable flexible thermocells with a wide operating temperature range

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2023-03, Vol.11 (13), p.6986-6996
• Main Authors: Peng, Peng, Li, Zhao, Xie, Daibin, Zhu, Kaihua, Du, Chunyu, Liang, Lirong, Liu, Zhuoxin, Chen, Guangming
• Format: Article
• Language: English
• Subjects: Adaptability; Aqueous electrolytes; Crystallization; Electrolytes; Environmental changes; Environmental conditions; Fabrication; Health hazards; High temperature; Humidification; Hydrogels; Immunological tolerance; Ion transport; Ions; Lithium ions; Molecular dynamics; Operating temperature; Packaging; Solid state; Temperature; Thermal energy
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta09385e

Thermocells (TECs) can directly convert thermal energy into electricity via the thermogalvanic effect of redox ions. The employment of hydrogel electrolytes allows for the facile fabrication of flexible quasi-solid-state TECs with low health hazard, easy scalability and eco-friendliness. In contrast, conventional hydrogel electrolytes cannot adapt to a sufficiently wide working temperature range, as they inevitably freeze under sub-zero temperatures and dry out under elevated temperatures, resulting in loss in both mechanical flexibility and ion transport capability. Herein, a hydrogel electrolyte using low-concentration redox ions with excellent freeze-tolerance and self-humidifying capabilities is rationally designed by regulating the hydration effect, affording a flexible quasi-solid-state aqueous TEC system that can continually work under a wide temperature range (−15 °C to 70 °C). It also demonstrates long-term environmental stability without the need for encapsulation or packaging. The colligative properties of the hydrogel electrolyte can suppress ice crystallization, and in-depth molecular dynamics simulations reveal that a vital underlying mechanism is the strong coordination effect of Li + ions with water molecules over a wide range of temperatures. The TEC designed in this work shows high adaptability to temperature fluctuations and environmental changes, and offers a promising route to promote low-grade heat harvesting under extreme environmental conditions. A flexible thermocell with good freeze-tolerance and self-humidifying capabilities is rationally designed. Its high adaptability to temperature fluctuations and environmental changes can promote low-grade heat harvesting under extreme conditions.